remove PowerReturnTypeResolver

You can't do "exact decimal" exponentiation. For the same reason that
sqrt() is of type Double in the JPA, pow(decimal, 0.5) is also of type
Double.

Yes, yes, I know that some dbs (Postgres!) claim that the return type is
NUMERIC for NUMERIC arguments. But go on, try it: yes, the return type of
typed NUMERIC, but then it has a very suspicious number of digits. Hrrm....
17 decimal digits, now why does that specific number ring a bell?

hibernate-core/src/main/java/org/hibernate/dialect/function/CommonFunctionFactory.java

@@ -1982,9 +1982,11 @@ public static void math(QueryEngine queryEngine) {
 				.register();
 
 		queryEngine.getSqmFunctionRegistry().namedDescriptorBuilder( "power" )
+				.setInvariantType(
+						queryEngine.getTypeConfiguration().getBasicTypeRegistry().resolve( StandardBasicTypes.DOUBLE )
+				)
 				.setExactArgumentCount( 2 )
 				.setParameterTypes(NUMERIC, NUMERIC)
-				.setReturnTypeResolver( new PowerReturnTypeResolver( queryEngine.getTypeConfiguration() ) )
 				.register();
 	}
 
@@ -2000,9 +2002,11 @@ public static void mod_operator(QueryEngine queryEngine) {
 
 	public static void power_expLn(QueryEngine queryEngine) {
 		queryEngine.getSqmFunctionRegistry().patternDescriptorBuilder( "power", "exp(ln(?1)*?2)" )
+				.setInvariantType(
+						queryEngine.getTypeConfiguration().getBasicTypeRegistry().resolve( StandardBasicTypes.DOUBLE )
+				)
 				.setExactArgumentCount( 2 )
 				.setParameterTypes(NUMERIC, NUMERIC)
-				.setReturnTypeResolver( new PowerReturnTypeResolver( queryEngine.getTypeConfiguration() ) )
 				.register();
 	}